In various prior-known plating processes, one or usually many articles to be plated are mounted in an electroplating cell as cathodes, one or more anodes are mounted in the cell in spaced relationship to the cathodes, a liquid electrolyte is circulated through the cell between the anodes and cathodes, and a plating potential is applied between the anodes and cathodes so as to plate metal from the electrolyte onto selected surfaces of the articles. In one typical example referred to as a box-plating process, gold is plated onto conductive metal areas of a plurality of "thin-film" circuit substrates from a circulating potassium gold cyanide plating solution, wherein a number of the substrates are mounted as cathodes in a plating tank in parallel between a plurality of facing inert anodes so that gold is deposited on the metallic areas of the substrates.
In this type of plating process involving continuous circulation of a liquid electrolyte between a number of parallel anodes interspersed between a number of parallel cathode substrates in a plating tank, problems are encountered in nonuniformity of the thickness of the plated metal between various areas along the surface of a single substrate and also between two different substrates positioned at different locations in the same tank. Such nonuniformity in plating thickness can lead to defective circuits where not enough metal or too much metal is deposited at any specified region. Such nonuniformity can also result in wastage of plated metal in that too much may be plated on many areas of the substrates in a batch to assure that the sparsest areas are sufficiently thick, which is particularly important in the plating of precious metals such as gold. In addition, such nonuniform plating can result in defects in the physical appearance of the plating, particularly in this type of gold plating process for depositing gold films of the order of 12,000 to 18,000 angstroms.